Technical Field
The present invention relates to a refrigerant circulation system, and more particularly relates to a system that circulates a refrigerant that cools an internal combustion engine.
Background Art
Conventionally, there has been disclosed a refrigerant circulation system that causes a refrigerant, which passes through a main body of an engine, to pass through three refrigerant circuits by an electronic control valve and return to the engine, for example, in JP 2013-234605 A. More specifically, the system includes the first refrigerant circuit provided with a radiator, the second refrigerant circuit provided with a heater, and the third refrigerant circuit provided with an oil cooler, and the electronic control valve includes three branch valves that open and close the respective refrigerant circuits. In the system, the opening degrees of the respective branch valves are independently controlled, and therefore, the flow rates of the refrigerant which is caused to flow into the respective refrigerant circuits can be individually controlled.
Further, JP 10-131753 A discloses a refrigerant circulation system including a refrigerant circuit in which a refrigerant flows, which is passed through both an engine and a radiator, a bypass channel that bypasses the radiator in a midpoint in the refrigerant circuit, and a flow rate control valve that is provided in the bypass channel. In the system, the flow rate control valve is configured by a valve housing, and a rotary type rotor that is installed in the valve housing to be capable of rotational operation. By rotating the rotor, opening and closing states of the refrigerant circuit and the bypass channel can be controlled.
Incidentally, when the electronic control valve in Patent Literature 1 described above is configured by the flow rate control valve in Patent Literature 3 described above, the installation space for the control valve can be saved. Further, the above described flow rate control valve is provided in the installation place of the above described electronic control valve, the opening and closing states of the respective refrigerant circuits can be controlled by rotation of the above described rotor. Therefore, the refrigerant is caused to flow into the oil cooler by opening the above described third refrigerant circuit at a time of start-up of the engine, for example, whereby the oil temperature is increased, and fuel efficiency can be enhanced. Further, the refrigerant is caused to pass through the heater by opening the above described second refrigerant circuit at a time of request for a heater, for example, whereby the in-vehicle air temperature can be increased. From the viewpoint like this, the present inventor is now conducting a study on control of the opening and closing states of the respective refrigerant circuits based on the operation plan in which the opening and closing states are set by being related with the rotation angle of the flow rate control valve from the reference position.
However, in the process of the study of the operation plan, it becomes clear that the following problem arises. That is to say, when the above described rotor is rotated based on the above described operation plan, there arises the situation where all of the refrigerant circuits are closed due to the structure of the above described rotor. Even if all of the refrigerant circuits are closed, no particular problem arises when the refrigerant has a low temperature. However, when the refrigerant has a high temperature, if all of the refrigerant circuits are closed, the refrigerant is not cooled and is likely to be boiled. Accordingly, it is not desirable that the all-closed state like this is brought about even if it is only temporary.